My post-war tender whistles fine when pushing the whistle button on my ZW transformer. However it intermitantly whistles in short bursts while running around the track when no whistle button is pushed. Any ideas why this happens and how it can be rectified?

With a PW or MPC era tender you will want to open it up and check the insulation that is under the soundboard.

If it is disintegrated/worn out, it will allow the board to short out, eventually it will burn the board up.  It's easy to replace it with either a piece of cardboard/posterboard or a piece of foam.  I had to replace the insulation on one of my tenders that had a similar problem.

Dave